RMIT飞行训练课件－Stalling RMIT 飞行训练失速课件

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RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 1 Brief 8
STALLING
Aim: To learn the principles and considerations of an aircraft approaching a stall, to
recognize the symptoms, and how to correctly recover with a minimum of height loss.
Application: - Inadvertent stall recovery, high AoA / low IAS operations such as
take-off and landing.
Revision:
 Aerofoil and Lift
 Drag
 Lift Distribution
A S
I A O A
Relative airflow
Angle of attack
Chordline
Slow Fast
DRAG
AIRSPEED
Induced Drag
Parasite drag
Minimum Drag TOTAL DRAG
Best L/D Ratio
Pressure distribution
+
_
Aerodynamic Force
Centre of pressure
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 2 Brief 8
Definitions:
 Critical Angle
- The AoA where the CL (the lifting ability of the wing) is at a maximum;
beyond that CL decreases markedly.
 Stall
- Occurs when the AoA exceeds the critical angle.
 Stall Speed (VS )
- The speed at which the aircraft stalls in the following configuration:-
MTOW @ mean sea level, idle power, straight and level altitude and the
most forward CoG position.
 Streamline Airflow
- Smooth airflow that remains attached to the surface of the aerofoil.
 Turbulent Airflow
- Airflow that cannot remain attached to the aerofoil, creating drag.
 Separation Point
- Where the streamline airflow becomes turbulent airflow.
 Boundary Layer
- The closest layers of air to the surface of the aerofoil which have reducing
velocities due to both the skin friction and the viscosity of the air. It is
initially laminar then transitions to become turbulent.
 Transition Region
- Where the laminar boundary layer becomes a turbulent boundary layer.
 Stagnation Point
- Point on the aerofoil where the airflow comes to rest relative to the
aerofoil. Normally occurs at the LE and the TE.
 Load Factor
- LF = L/W, measured in ‘g’ numbers.
AoA
CL
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 3 Brief 8
Principles:
Let’s take a closer look at an aerofoil at varying AoA’s:
 4 AoA
- Airflow is streamlined with the transition and separation occurring well aft.
Referring to the pilot’s lift formula, most of the lift produced is due to high
airspeed, whilst only a small amount is due to the AoA.
 8 AoA
- With the increased AoA comes a further decrease in Pstatic over the
leading section of the aerofoil. Hence the average pressure moves
forward (acting through the CoP), thereby causing an earlier transition
region and separation point.
 16 AoA
- At the critical AoA, the lift produced due to the AoA is a maximum and the
CoP is the furthest forward. This causes even earlier separation, creating
more drag and an adverse pressure gradient towards the trailing edge.
 16 AoA
- Whilst the aerofoil is still creating some lift, but is insufficient to sustain the
weight. Most of the airflow is turbulent with a rearwards shift in CoP
position, causing a nose drop and loss of altitude
IAS
IAS IAS IAS
CL
CL
CL
CL
L
L L L
W W W W
110kt
4o
70kt
8o
44kt
16o
<44kt
>16o IAS
AoA
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 4 Brief 8
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 5 Brief 8
The stall AoA can be associated with a particular airspeed, since we can’t directly
read AoA (Performance = Power + Attitude):
VS0 = 33KIAS (full flap)
VS1 = 44KIAS (clean)
Usual Symptoms:
1. High nose attitude
2. Low IAS
3. Reduced control effectiveness
4. Stall warning
5. Control buffet
Considerations:
 Manoeuvres
- When pulling out of a dive, applied back pressure,  AoA,  L hence LF.
- The stall speed in a manoeuvre can be calculated using
VNS = VS  LF
- In addition to that, the load factor in a turn can be calculated using
LF = 1 / Cos(AoB)
eg. In a steep turn: AoB = 60  LF = 2g so, VNS = 62KIAS
A stall occurs at an AoA, not an IAS
Actual Stalled Flightpath
Attempted 3G
Pullout
Planned
Flightpath
Increased
Stall Speed
1G 2G 3G 4G
2.0
1.8
1.6
1.4
1.2
1.0
“g” load
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 6 Brief 8
 Weight
- As weight increases, lift must also increase. When both aircraft achieve
the critical angle the heavy aircraft must fly at increased IAS to produce
the additional lift required.
 CoG
- Forward movement of the CoG will increase the strength of the nosedown
couple between lift and weight as a result increase the amount of
downforce required on the tailplane
- In effect this increase of downforce is similar to an increase in weight and
therefore a forward CoG will lead to an increased stall speed.
 Ice
- Ice disturbs the streamline airflow causing earlier separation.
- Also  W, which requires  L hence  VS.
L
L
W
W
16o 16o
40 kt 44 kt
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 7 Brief 8
 Flap
- Lowering flap increases the aerofoil’s camber and AoA for the same
attitude. Therefore at the same AoA (ie. critical angle) the flaps allow the
aircraft to fly at  IAS with a lower nose attitude.
- With flap, more lift is generated on the inboard portions of wing (closer to
CoG), reducing lateral stability and becoming more susceptible to a
wingdrop.
 Power
- Slipstream re-energises the airflow over the inboard sections of the wing,
delaying separation. Also the vertical component of thrust assists in
counteracting the weight.
- Like flaps, the wingtip may stall first (due less airflow) causing a wingdrop.
 Stability in the Stall
- Reduces the angle of incidence on wingtip compared to the wing root.
- Ensures the wing root stalls first providing control buffet on the elevator
and a more stable stall.
16o 16o Relative Airflow
High Nose Attitude Lower Nose Attitude
Thrust
TH
TV
Smaller AoA
Relative Larger AoA
Airflow Cross-Section
at Wing Tip
Cross-Section
at Wing Tip
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 8 Brief 8
Air Exercise:
 Pre-Stalling Checks
- Height sufficient to recover by 3000ft
- Hatches/Harnesses secure.
- Engine Temperature & Pressure.
- Location – not above a populated area.
- Loose articles secure.
- Lookout (360 turn)
 Entry
- Pick a reference point (maintain with rudder not ailerons)
- Retard throttle, maintaining height.
- Note previously discussed symptoms.
 Stall
- Nose pitches down.
- Note height loss
 Recovery
- Lower nose to horizon.
- Speed increases through 65KIAS, full power.
- Climb out.
 Wing Drop Recovery
- Apply opposite rudder to stop yaw.
- Lower nose to unstall attitude.
- Passing 65KIAS, full power.
- Climb out.
Airmanship:
- INADVERTANT STALLS SHOULD NEVER OCCUR!
- Lookout (conduct 90 turn after each stall).
- Smooth co-ordinated control input – especially during recovery.
- Correct Handover/Takeover procedure.
- Monitor engine gauges.

cdzfk

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